Two-Dimensional Velocity of the Magnetic Structure Observed on July 11, 2017 by the Magnetospheric Multiscale Spacecraft

In order to determine particle velocities and electric field in the frame of the magnetic structure, one first needs to determine the velocity of the magnetic structure in the frame of the spacecraft observations. Here, we demonstrate two methods to determine a two-dimensional magnetic structure velocity for the magnetic reconnection event observed in the magnetotail by the Magnetospheric Multiscale (MMS) spacecraft on July 11, 2017, Spatio-Temporal Difference (STD) and the recently developed polynomial reconstruction method. Both of these methods use the magnetic field measurements; the reconstruction technique also uses the current density measured by the particle instrument. We find rough agreement between the results of our methods and with other velocity determinations previously published. We also explain a number of features of STD and show that the polynomial reconstruction technique is most likely to be valid within a distance of 2 spacecraft spacings from the centroid of the MMS spacecraft. Both of these methods are susceptible to contamination by magnetometer calibration errors.

Automated summary

Two methods, Spatio-Temporal Difference (STD) and polynomial reconstruction, are demonstrated for determining the two-dimensional magnetic structure velocity in a magnetic reconnection event observed by the Magnetospheric Multiscale (MMS) spacecraft. Both methods utilize magnetic field measurements, with the reconstruction technique also incorporating current density measurements from particle instruments. There is general agreement between the results of these methods and previously published velocity determinations, but both are susceptible to contamination by magnetometer calibration errors.